GenusZapusCoues
Genotype.—Dipus hudsoniusZimmerman.
External characters.—Muriform in general appearance; forelimbs small, short; hind limbs greatly developed; hind feet long and narrow; tail tapering, attenuate, subcylindrical; head long and mouse-shaped; eyes small and situated midway between nose and ear; external ear somewhat longer than surrounding hair and provided with antitragal flap which can cover external auditory meatus, and in company with tragus completely close opening; upper lip without median groove; internal cheek-pouches well developed and opening at corners of mouth; mystacial vibrissae conspicuous; supercilliary vibrissae few; genal tuft absent; teats normally eight and arranged in pairs (one pectoral, two abdominal, and one inguinal); anterior and posterior pairs frequently undeveloped; general pelage coarse; color of pelage varies somewhat in different species but always follows single basic pattern of broad dorsal band of some shade of brown or brownish-yellow darkened with brownish-black, sides of a lighter tone and slightly streaked with brownish-black, underparts snow-white, sometimes suffusedwith color of the sides and usually separated from color of sides by sharp line of clear brownish-yellow; backs of forefeet and hind feet grayish-white; tail distinctly bicolor, dark brown above and yellowish-white below; ears dark and narrowly edged with light color.
Fig. 44.Map showing distribution of the genusZapus.
Fig. 44.Map showing distribution of the genusZapus.
Cranial characters.—Skull short in relation to width, deep relative to other dimensions, somewhat convex; delicate, papery, without strong angularity; braincase relatively unexpanded; antorbital foramen obliquely oval and transmits masseter muscle of great size; foramen in inferior ramus of zygomatic process of maxillary for passage of superior maxillary branch of trigeminal nerve small; zygomata not wide-spreading; underside of zygoma nearly horizontal, upper edge anteriorly rises prominently owing to extension of jugal upward along maxillary; jugal and lachrymal in contact; one ramus of zygomatic process of maxilla arises directly above other; rostrum thick basally and relatively attenuate distally; ends of nasals project noticeably beyond incisors; premaxillaries develop strong alveolar plate separating superior incisors for half their length; palatal bones shortened posteriorly, free edge often concave; incisive foramina long, broad, and separated by bulbose (except at posterior end) bony septum; mastoid bullae absent; auditory bullae short and transversely placed; postorbital process never present; parietals nearly square, sometimes emarginate in front; angle of mandible flattened and bent inward; coronoid process weak, acute, and slopes strongly upward.
Dental characters.—Dental formula
I 1
C O
P 1
M 3
i 1
c o
p o
mv 3
upper incisors short, compressed, curved backward, and strongly grooved; lower incisors slender, curved backward, and ungrooved; both upper and lower incisors deep orange or yellow; four upper cheek-teeth present; premolar small, single rooted and, sometimes, non-functional; upper molars tri-rooted, sub-hypsodont, and with occlusal surface non-cuspidate (flat); enamel pattern, much complicated, consisting of one main re-entrant fold lingually and four re-entrant folds labially; three lower molars, bi-rooted, sub-hypsodont, flat crowned, with two outer and four inner re-entrant folds.
Postcranial characters.—Neck short and weak; atlas large; axis separate from atlas; remaining (5) cervical vertebrae also free; thoracic (12) and lumbar (7) vertebrae strongly built; posterior lumbars with enlarged neural and anteriorly directed transverse processes; sacral vertebrae (7) as in murids; caudal vertebrae variable in number (average 36); clavicle long, slender, uniformly curved, convex outwardly; scapula with supraspinous and infraspinous fossae of equal size; forelimbs short, approximately half as long as hind limbs; hind limbs elongate, slender; femur with third trochanter; tibia and fibula fused slightly distal to middle of former; five elongate, separate metatarsals (first and fifth subequal, shorter than others).
ARTIFICIAL KEY TO THE SPECIES OF THE GENUS ZAPUS
SYSTEMATIC ACCOUNTS OF SPECIES AND SUBSPECIES
Zapus trinotatusRhoads
(Synonymy under subspecies)
Range.—From southwestern British Columbia southward through western Washington and Oregon and in the humid coastal district of California almost to the Golden Gate (seefig. 45).
Characters of the species:External.—Size medium to large (total length 221 mm to 238 mm); tail longer than head and body (131 mm to 149 mm) and bicolored, brown above, white to yellowish-white below; hind feet long (31 mm to 34 mm), grayish-white above; back various hues and tones of ochraceous and tawny; sides paler than back; lateral line separating sides from ventral surface usually distinct and bright; ventral coloration white, usually with suffusion of ochraceous; ears usually dark, sometimes flecked, and usually narrowly edged with color of sides; guard hairs average 141 microns (133u to 155u) in diameter; underhair with medullary pigment in narrow, hollow rectangles; cuticular scales of underhair smaller and more numerous than in other species.
Baculum.—Size large (total length 6.7 mm to 7.4 mm); base broad (0.7 mm to 0.9 mm); tip broad (0.44 mm to 0.57 mm); spade-shaped in dorsal aspect and tilted upward, gradually tapering to thin-edged tip; shaft rounded, straight.
Skull.—Large, broad and deep in relation to length; pterygoid fossa broad; anterior ramus of zygomatic process of maxillary relatively narrow; nasofrontal juncture relatively broad; coronoid process of mandible elongate. Upper premolars relatively large (averaging .70 mm in length and .75 mm in width), usually functional, occlusal surface with labial re-entrant fold forming crescentine loop incompletely enclosing single central cusp; m3 relatively large, elongated; m1 elongated, broadly rounded anteriorly.
GEOGRAPHIC VARIATION
There are four subspecies currently recognized, all of which are confined to the Pacific coastal region of North America (Seefig. 45). The features that vary geographically are external size, color of pelage (shade and tone of upper parts and tint of lower parts), and dimensions of certain cranial structures (zygomata, braincase, incisive foramina, palatal bridge, auditory bullae, and pterygoid fossae).
External size is smallest in the southernmost geographic race (Z. t. orarius) and largest in the northernmost geographic race (Z. t. trinotatus). This decrease in size from north to south is clinal and is in keeping with Bergman’s Rule which postulates that within one species the smallest individuals occur in the warmer parts of its geographic range.
Fig. 45.Map showing distribution ofZapus trinotatus.1.Z. t. eureka2.Z. t. montanus3.Z. t. orarius4.Z. t. trinotatus
Fig. 45.Map showing distribution ofZapus trinotatus.
Coloration of pelage is geographically variable. There is a gradual change in the color of the pelage from north to south. Animals obtained in the northern part of the geographic range ofZ. trinotatusare generally darker dorsally (more tawny) with the ventral pelage usually pure white. Those individuals from the southern part of the geographic range ofZ. trinotatushave the dorsal pelage lighter (more reddish and yellow-brown) and ventrally the pelage is usually heavily suffused with reddish-brown. The crania also vary geographically; they are largest in the northernmost part of the range of the species and smallest in the southernmost part.
NATURAL HISTORY
Habitat.—On the Olympic Peninsula, Washington, in 1931 Svihla and Svihla (1933:132) found this species equally abundant in alpine meadows near timberline, in open grassy areas, and in tall meadow grass and low blueberry bushes. All of the mice were in wet marshy places. Bailey (1936:232) reported that in Oregon, these mice live in meadows, marshes, under ferns and weeds in the woods, or near mountain brooks and streams. Taylor (1922:221) foundZapusin moderately moist meadows in the Hudsonian Life-zone at Mt. Rainier, Washington, and Dice (1932:49) found them in deciduous forest and in open, grassy, or sphagnum bogs. Dice records it as common also among the alders and willows in high, open, grassy parks. Merriam (1897b:223) foundZ. trinotatusabundantly in moist places grown-over with grass or weeds. Grass cuttings two to three inches long were left in small heaps at feeding sites and indicate the presence of these mice.
Behavior.—Svihla and Svihla (1933:131) write that the long tail ofZ. trinotatusis used as a balancing organ when the mouse is in motion. A tailless mouse, attempting to escape, turned somersaults in the air and invariably landed on its back; the loss of its tail seemed to leave the mouse without compensation for the vigorous push of the hind legs. Dalquest (1948:371) noted that the jumping mouse sometimes walks on all fours, but ordinarily moves by means of short hops on the hind feet alone. When startled, jumping mice travel in bounds of six feet or more at a jump.
Zapus trinotatus, according to Bailey (1936:232) and Elliot (1899:261), is mainly nocturnal but occasionally is active in daylight.
Svihla and Svihla (op. cit.:132) heard captive animals make squeaking noises when fighting. On several occasions captive animalsmade a drumming noise by rapidly beating the tail against a resonant body such as the bottom of a tin can.
Concerning hibernation, Bailey (loc. cit.) remarks that animals of this species in Oregon, become fat in early autumn and lay down excess adipose tissue under the skin, over the muscles, and in the abdominal cavity. Svihla and Svihla (op. cit.:133) noted that captives from the Olympic Peninsula, Washington, gained weight in September and October and became extremely fat. With the additional weight they were more listless and drowsy, often spending days curled up in the hibernating position with the head between the hind legs and the long tail curled completely over the head and body. Warmth aroused the animals to activity, but when the temperature dropped they again hibernated. Flahaut (1939:17) reported the discovery on February 23, 1939, at Henderson Inlet, South Bay, Thurston County, Washington, of two nest cavities inhabited by jumping mice that were hibernating. The nests, four inches apart and 30 inches below the surface of the ground, were approximately five inches in diameter and made of shredded paper. Both mice were dormant, covered by nesting materials and curled up in the aforementioned hibernating posture. Dalquest (1948: 371) writes that in the lowlands of Washington this species disappears by late July but that in the mountains it remains active until the middle of September. Edson (1932:56) records an individual taken on April 20 from its place of hibernation beneath the roots of a decaying stump. This animal quickly roused in the warm mid-afternoon sun but became dormant again when the temperature dropped to 45° F. It seems that animals near the end of hibernation become active on warm days and return to the torpid state on cold ones.
Enemies.—Little is recorded concerning enemies ofZ. trinotatus, but Bailey (1936:233) lists owls and other nocturnal birds, weasels, skunks, and badgers as preying on this mouse. Smith and Hopkins (1937:191) foundZ. t. orariusin barn owl pellets obtained in Elk Valley, Marin County, California.
Food.—Bailey (loc. cit.) remarks that in Oregon, these mice feed mainly on small seeds of grasses, small grains (wheat, barley, oats, and rye), and other plants. These seeds are obtained by cutting the stems, drawing the stems down and biting off lower sections until the seed-laden heads are reached. Bailey (op. cit.:234) found thattrinotatusutilized also the seeds of the western skunk cabbage.
Near Seattle, Washington, according to Dalquest (loc. cit.), the principal food ofZ. trinotatuswas velvet grass (Holchus lanatus),broad-leaved dock, and the seeds of other grasses. Dalquest reports also that the fruit of the blackberry (Rubus macropelatus) is eaten and that an occasional jumping mouse has its chin stained a deep purple by juice from these berries.
Reproduction.—There is normally a single litter of from four to eight young per year according to Bailey (loc. cit.). Newly born young have been described by Svihla and Svihla (1933:132) as follows: slightly smaller than newly born harvest mice (Reithrodontomys m. megalotis), average weight .8 grams, hairless (without even vibrissae visible), pink, eyes closed, ears folded, heads short and stubby, tails long (longer than those of newly bornPeromyscus), and bodies surprisingly small (when compared with newly bornPeromyscus maniculatus).
Zapus trinotatus eurekaA. B. Howell
Zapus trinotatus eurekaA. B. Howell, Univ. California Publ., Zool. 21:229, May 20, 1920.
Zapus trinotatus trinotatus, Preble, N. Amer. Fauna, 15:26, August 8, 1899 (part—the part from Crescent City and Carsons Camp, Mad River, California).
Zapus orariusPreble, N. Amer. Fauna, 15:29, August 8, 1899 (part—the part from Eureka and Carsons Camp, Mad River, California).
Type.—Female, adult, skin and skull, No. 11703, Mus. Vert. Zool.; Fair Oaks, Humboldt County, California; obtained on August 27, 1910, by Joseph S. Dixon, original No. 1743.Range.—Northwestern coastal region of California, from Russian Gulch State Park, Mendocino County north to Trinidad, Humboldt County. Zonal range: humid Transition.Description.—Size medium; color dull; back near Ochraceous-Buff with heavy admixture of black hairs, forming broad dorsal band; sides from near Ochraceous-Buff to near Ochraceous-Salmon, sometimes with heavy admixture of black hairs; lateral line usually distinct, sometimes blending with color of belly and side; ventral surface usually suffused with color of sides; tail bicolored, dark brown above, white to yellowish-white below; feet grayish-white above; ears dark, edged with color of sides; auditory bullae large; pterygoid fossae broad; incisive foramina relatively short; palatal bridge short; maxillary tooth-rows relatively short; narrow across zygomata; braincase narrow; interorbital region narrow; zygomatic arch relatively short.Comparisons.—FromZapus trinotatus trinotatus,Z. t. eurekadiffers in: Size smaller; ventral surface with much greater suffusion of ochraceous; auditory bullae larger; pterygoid fossae relatively broader; frontal region less inflated; palatal bridge shorter; braincase narrower; narrow across zygomata; upper tooth-rows shorter.For comparison withZapus trinotatus orariussee account of that subspecies.
Type.—Female, adult, skin and skull, No. 11703, Mus. Vert. Zool.; Fair Oaks, Humboldt County, California; obtained on August 27, 1910, by Joseph S. Dixon, original No. 1743.
Range.—Northwestern coastal region of California, from Russian Gulch State Park, Mendocino County north to Trinidad, Humboldt County. Zonal range: humid Transition.
Description.—Size medium; color dull; back near Ochraceous-Buff with heavy admixture of black hairs, forming broad dorsal band; sides from near Ochraceous-Buff to near Ochraceous-Salmon, sometimes with heavy admixture of black hairs; lateral line usually distinct, sometimes blending with color of belly and side; ventral surface usually suffused with color of sides; tail bicolored, dark brown above, white to yellowish-white below; feet grayish-white above; ears dark, edged with color of sides; auditory bullae large; pterygoid fossae broad; incisive foramina relatively short; palatal bridge short; maxillary tooth-rows relatively short; narrow across zygomata; braincase narrow; interorbital region narrow; zygomatic arch relatively short.
Comparisons.—FromZapus trinotatus trinotatus,Z. t. eurekadiffers in: Size smaller; ventral surface with much greater suffusion of ochraceous; auditory bullae larger; pterygoid fossae relatively broader; frontal region less inflated; palatal bridge shorter; braincase narrower; narrow across zygomata; upper tooth-rows shorter.
For comparison withZapus trinotatus orariussee account of that subspecies.
Remarks.—Howell (1920:230), without having examined the material, provisionally referred specimens from Requa and Crescent City, Del Norte County, California, toZ. t. eureka. I have studiedthis material and find the specimens to be intermediate betweenZ. t. trinotatusandZ. t. eurekain cranial characters (zygomatic breadth, interorbital width, and breadth of braincase), but nearerZ. t. trinotatusin coloration (absence of ochraceous suffusion ventrally). They are here referred toZ. t. trinotatus. The zone of intergradation betweenZ. t. trinotatusandZ. t. eurekaseems to extend from Requa, California, north to Gold Beach, Oregon, where other specimens intermediate between these two subspecies, have been obtained. These individuals are also referred toZ. t. trinotatuson the basis of cranial features and color.
Specimens examined.—Total, 42, all from California, distributed as follows:Humboldt Co.: Trinidad, 4 (SDM); Carsons Camp, Mad River, 3 (USBS); 3 mi. W Arcata, 5 (MVZ);73/10mi. E Bayside, 1 (MVZ);12 mi. S Korbel, on Maple Creek, 2 (MVZ);Falk, 1 (MVZ); Carlotta, 1 (MVZ);F. B. Summer Redwoods, S Eureka, 1 (MVZ);Maple Creek, 1 mi. W junction Mad River, 12 (MVZ).Mendocino County: Mendocino City, 1 (MVZ); Albion River,1/3mi. E MacDonalds Ranch, 1 (MVZ); Russian Gulch State Park, 10 (MVZ).Marginal records.—California: Trinidad; Russian Gulch State Park; Albion River,1/3mi. E MacDonalds Ranch; Mendocino City; Carlotta.
Specimens examined.—Total, 42, all from California, distributed as follows:Humboldt Co.: Trinidad, 4 (SDM); Carsons Camp, Mad River, 3 (USBS); 3 mi. W Arcata, 5 (MVZ);73/10mi. E Bayside, 1 (MVZ);12 mi. S Korbel, on Maple Creek, 2 (MVZ);Falk, 1 (MVZ); Carlotta, 1 (MVZ);F. B. Summer Redwoods, S Eureka, 1 (MVZ);Maple Creek, 1 mi. W junction Mad River, 12 (MVZ).Mendocino County: Mendocino City, 1 (MVZ); Albion River,1/3mi. E MacDonalds Ranch, 1 (MVZ); Russian Gulch State Park, 10 (MVZ).
Marginal records.—California: Trinidad; Russian Gulch State Park; Albion River,1/3mi. E MacDonalds Ranch; Mendocino City; Carlotta.
Zapus trinotatus montanusMerriam
Zapus trinotatus montanusMerriam, Proc. Biol. Soc. Washington, 11:104, April 26, 1897; Bailey, N. Amer. Fauna, 55:234, August 29, 1936.
Zapus montanus, Preble, N. Amer. Fauna, 15:28, August 8, 1899.
Type.—Female, adult, skin and skull; No. 79863, U. S. Nat. Mus., Biol. Surv. Coll.; Crater Lake, Klamath County, Oregon; obtained on August 19, 1896, by Edward A. Preble, original No. 1388.Range.—From Crater Lake, Klamath County, Oregon, northward along the Cascade Range into Hood River County, Oregon. Zonal range: Transition and Canadian.Description.—Size medium; back near Ochraceous-Buff with admixture of black hair, resulting in a grizzled, broad, dorsal band; sides lighter than back, from near Ochraceous-Buff to near Pinkish-Cinnamon, and lined with black hair; lateral line distinct; underparts usually pure white, sometimes with slight suffusion of ochraceous on lower throat and upper chest; tail bicolored, brown above and yellowish-white below; ears dark, sometimes flecked with ochraceous, edged with yellowish-white; feet grayish-white above; braincase relatively narrow; zygomata relatively short; condylobasal length short; mastoid region relatively narrow; palatal bridge short; auditory bullae large; frontal region inflated; pterygoid fossae relatively narrow.Comparison.—FromZapus trinotatus trinotatus,Z. t. montanusdiffers as follows: Size averaging smaller; sides more ochraceous, fewer black hairs; upper parts duller; skull smaller; zygomatic arch shorter, braincase relatively narrower; frontal region more inflated; pterygoid fossae relatively narrower; zygomata narrower.
Type.—Female, adult, skin and skull; No. 79863, U. S. Nat. Mus., Biol. Surv. Coll.; Crater Lake, Klamath County, Oregon; obtained on August 19, 1896, by Edward A. Preble, original No. 1388.
Range.—From Crater Lake, Klamath County, Oregon, northward along the Cascade Range into Hood River County, Oregon. Zonal range: Transition and Canadian.
Description.—Size medium; back near Ochraceous-Buff with admixture of black hair, resulting in a grizzled, broad, dorsal band; sides lighter than back, from near Ochraceous-Buff to near Pinkish-Cinnamon, and lined with black hair; lateral line distinct; underparts usually pure white, sometimes with slight suffusion of ochraceous on lower throat and upper chest; tail bicolored, brown above and yellowish-white below; ears dark, sometimes flecked with ochraceous, edged with yellowish-white; feet grayish-white above; braincase relatively narrow; zygomata relatively short; condylobasal length short; mastoid region relatively narrow; palatal bridge short; auditory bullae large; frontal region inflated; pterygoid fossae relatively narrow.
Comparison.—FromZapus trinotatus trinotatus,Z. t. montanusdiffers as follows: Size averaging smaller; sides more ochraceous, fewer black hairs; upper parts duller; skull smaller; zygomatic arch shorter, braincase relatively narrower; frontal region more inflated; pterygoid fossae relatively narrower; zygomata narrower.
Remarks.—The systematic status ofZ. t. montanushas been in doubt. Several workers, for example, Howell (1920:227) andPreble (1899:28), considered it to be a species, and others (Merriam, 1897a:104, Bailey, 1936:234) considered it to be a subspecies ofZ. trinotatus.Z. montanusis here considered to be a subspecies ofZ. trinotatus, because of the agreement of the two in size and shape of the baculum, diameter and pigment pattern of the hair, and the over-all proportions of the skull. In addition, animals from intermediate geographic areas are available and show actual intergradation.
Intergradation has been noted in specimens from North Santiam River, 3400 ft., Oregon. In color, in length of incisive foramina, in breadth of braincase, and in width of zygomata these specimens are intermediate betweenZapus trinotatus montanusandZ. t. trinotatus, but in the sum-total of characters they are referable to the former. Specimens from Lost Creek R. S., 10 mi. SE McKenzie Bridge, are intermediate in color betweenZ. t. trinotatusandZ. t. montanus; they are referable toZ. t. montanus. The animals available from Brooks Meadow, 4300 ft., 9 mi. ENE Mt. Hood and the one from Mt. Hood, in color, in length of incisive foramina, and in mastoid width, closely approachZ. t. trinotatusfrom Skamania County, Washington, but in the sum-total of characters are nearestZ. t. montanusand are here referred tomontanus.
Specimens examined.—Total, 35, all from Oregon, distributed as follows:Deschutes County: Tumalo Creek, 15 mi. W Bend, 6100 ft., 3 (MVZ).Douglas Co.: Diamond Lake, 1 (USBS).Hood River Co.: Brooks Meadow, 4300 ft., 9 mi. ENE Mt. Hood, 10 (MVZ);Mt. Hood, 1 (USBS).Klamath Co.:Crater Lake, 3 (MVZ);1/2mi. N Government Camp, 6700 ft., Munson Valley, Crater Lake Nat’l Park, 2 (MVZ); east slope Cascade Divide, 6400 ft., Crater Lake Nat’l Park, 2; Anna Creek, Mt. Mazama, 6000 ft., 2 (USBS).Lane Co.: Lost Creek R. S., 10 mi. SE McKenzie Bridge, 6 (USBS);Three Sisters, Alder Springs, 4300 ft., 2 (USBS).Linn County: North Santiam River, 3400 ft., 3 (MVZ).Marginal records.—Oregon: Brooks Meadow, 4300 ft., 9 mi. ENE Mt. Hood; Tumalo Creek, 15 mi. W Bend, 6100 ft.; Anna Creek, Mt. Mazama, 6000 ft.; east slope Cascade Divide, 6400 ft., Crater Lake Nat’l Park; Diamond Lake; North Santiam River, 3400 ft.
Specimens examined.—Total, 35, all from Oregon, distributed as follows:Deschutes County: Tumalo Creek, 15 mi. W Bend, 6100 ft., 3 (MVZ).Douglas Co.: Diamond Lake, 1 (USBS).Hood River Co.: Brooks Meadow, 4300 ft., 9 mi. ENE Mt. Hood, 10 (MVZ);Mt. Hood, 1 (USBS).Klamath Co.:Crater Lake, 3 (MVZ);1/2mi. N Government Camp, 6700 ft., Munson Valley, Crater Lake Nat’l Park, 2 (MVZ); east slope Cascade Divide, 6400 ft., Crater Lake Nat’l Park, 2; Anna Creek, Mt. Mazama, 6000 ft., 2 (USBS).Lane Co.: Lost Creek R. S., 10 mi. SE McKenzie Bridge, 6 (USBS);Three Sisters, Alder Springs, 4300 ft., 2 (USBS).Linn County: North Santiam River, 3400 ft., 3 (MVZ).
Marginal records.—Oregon: Brooks Meadow, 4300 ft., 9 mi. ENE Mt. Hood; Tumalo Creek, 15 mi. W Bend, 6100 ft.; Anna Creek, Mt. Mazama, 6000 ft.; east slope Cascade Divide, 6400 ft., Crater Lake Nat’l Park; Diamond Lake; North Santiam River, 3400 ft.
Zapus trinotatus orariusPreble
Zapus orariusPreble, N. Amer. Fauna, 15:29, August 8, 1899.
Zapus pacificusMerriam, Proc. Biol. Soc. Washington, 11:104, April 26, 1897 (part—the part from Point Reyes, Marin County, California).
Zapus trinotatus orarius, Hooper, Miscl. Publ. Mus. Zool. Univ. Michigan, 59:67, January 12, 1944.
Type.—Male, adult, skin and skull, No. 250, collection of E. A. and O. Bangs (now in Mus. Comp. Zool.); Point Reyes, Marin County, California; obtained on May 14, 1893, by C. A. Allen, original No. 618.Range.—Southern and western Marin County, California. Zonal range: Upper Sonoran areas that are moist yet safe from continuous inundation.[392]Description.—Size small; back dark ochraceous, usually overlaid with black hairs forming broad dorsal band; side lighter than back with admixture of black hairs; lateral line distinct, usually bright, near Ochraceous-Buff; under parts strongly suffused with ochraceous; tail bicolored, white to yellowish-white below and dark brown above; feet grayish-white above; ears dark, edged with yellowish-white or tan; skull small; zygomata narrow; braincase narrow; maxillary tooth-rows short; interorbital region narrow; incisive foramina short; palatal bridge relatively long; mastoid region relatively broad; occipitonasal length short.Comparison.—FromZapus trinotatus eureka,Z. t. orariusdiffers in: Size smaller; color, dorsally and laterally, brighter, more ochraceous; skull averaging smaller in all measurements taken except length of palatal bridge, where it averages longer; auditory bullae smaller, less inflated; pterygoid fossae narrower.
Type.—Male, adult, skin and skull, No. 250, collection of E. A. and O. Bangs (now in Mus. Comp. Zool.); Point Reyes, Marin County, California; obtained on May 14, 1893, by C. A. Allen, original No. 618.
Range.—Southern and western Marin County, California. Zonal range: Upper Sonoran areas that are moist yet safe from continuous inundation.
[392]
Description.—Size small; back dark ochraceous, usually overlaid with black hairs forming broad dorsal band; side lighter than back with admixture of black hairs; lateral line distinct, usually bright, near Ochraceous-Buff; under parts strongly suffused with ochraceous; tail bicolored, white to yellowish-white below and dark brown above; feet grayish-white above; ears dark, edged with yellowish-white or tan; skull small; zygomata narrow; braincase narrow; maxillary tooth-rows short; interorbital region narrow; incisive foramina short; palatal bridge relatively long; mastoid region relatively broad; occipitonasal length short.
Comparison.—FromZapus trinotatus eureka,Z. t. orariusdiffers in: Size smaller; color, dorsally and laterally, brighter, more ochraceous; skull averaging smaller in all measurements taken except length of palatal bridge, where it averages longer; auditory bullae smaller, less inflated; pterygoid fossae narrower.
Remarks.—Preble (1899:30) named this jumping mouse as a full species. Included in the specimens examined were animals from Eureka and Mad River, Humboldt County, California. Howell (1920:231) retainedZ. orariusas a full species but restricted its range to Marin County, California, and referred material from northern California, including the animals from Eureka and Mad River, to a new subspecies (eureka) of the speciesZ. trinotatus. Howell (loc. cit.) suggested thatZ. orariushad its closest affinity withZ. t. eurekabut remarked that intergrading material was not available. Hooper (1944:68) arrangedZ. orariusas a subspecies ofZ. trinotatusand suggested that intergrades could be expected from geographically intermediate areas, for example, northern Sonoma County, California.
Although animals from intermediate geographic areas still are not available to show actual intergradation, I concur with Hooper (loc. cit.) and arrangeZ. orariusas a subspecies ofZ. trinotatus. The close relationship ofZ. orariustoZ. trinotatusis evident; certain diagnostic characters, held in common, are the shape and size of the os penis, the diameter and pigment pattern of the hair, and the general configuration of the skull.
Interbreeding in the wild betweenZ. t. orariusandZ. t. eurekaprobably does not take place, because these subspecies are separated by terrain unsuited to jumping mice.
Specimens examined.—Total, 29, all from California, distributed as follows:Marin County(MVZ): 3 mi. W Inverness, 300 ft., 14;5 mi. NNE Point Reyes Lighthouse, 12;W end Elk Valley, 10 ft., 1; West Portal, Fort Barry, 2.Marginal records.—California: 3 mi. W Inverness, 300 ft.; West Portal, Fort Barry.
Specimens examined.—Total, 29, all from California, distributed as follows:Marin County(MVZ): 3 mi. W Inverness, 300 ft., 14;5 mi. NNE Point Reyes Lighthouse, 12;W end Elk Valley, 10 ft., 1; West Portal, Fort Barry, 2.
Marginal records.—California: 3 mi. W Inverness, 300 ft.; West Portal, Fort Barry.
Zapus trinotatus trinotatusRhoads
Zapus trinotatus Rhoads, Proc. Acad. Nat. Sci. Philadelphia, 1894:42, January 15, 1895.
Jaculus hudsonius, Baird, Repts. Expl. and Surv. 111, 8 (pt. 1): 433, July 14, 1858 (part—the part from Washington).
Zapus hudsonius, Coues, Bull. U. S. Geol. and Geog. Surv. of the Territories, 2nd ser., No. 5:260, 1877 (part—the part from Steilacoom [Pierce County], Washington).
Zapus imperatorElliot, Field Columbian Mus., publ. 30, zool. ser., 1:228, February 1, 1899, type from Siegs Ranch, Elwah River, Clallam County, Washington.
Zapus princeps trinotatus, Dalquest, Univ. Kansas Publ. Mus. Nat. Hist., 2:371, April 9, 1948.
Type.—Male, adult, skin and skull, No. 360, S. N. Rhoads Coll.; Lulu Island, mouth of Frazer River, British Columbia; obtained on May 31, 1892, by S. N. Rhoads (type in Philadelphia Acad. Nat. Sci.).Range.—Pacific coastal region from Requa, Del Norte County, California, north in Oregon west of the Cascades, and in Washington including the Cascades; to southwestern British Columbia.Description.—Size large; back from near Ochraceous-Buff to near Tawny with admixture of black hair forming broad dorsal band; sides lighter than back from near Ochraceous-Buff to near Tawny; lateral line usually distinct; belly white, sometimes with faint suffusion of ochraceous on lower throat and upper chest; tail bicolored, brown above, white to yellowish-white below; ears dark, sometimes flecked with color of sides, edged with ochraceous; feet grayish-white above; palatal bridge relatively short; incisive foramina relatively long; condylobasal region long; zygomatic width great; braincase relatively broad; distance from incisors to postpalatal notch relatively great.Comparisons.—For comparisons withZapus trinotatus montanusandZapus trinotatus eurekasee accounts of those subspecies.
Type.—Male, adult, skin and skull, No. 360, S. N. Rhoads Coll.; Lulu Island, mouth of Frazer River, British Columbia; obtained on May 31, 1892, by S. N. Rhoads (type in Philadelphia Acad. Nat. Sci.).
Range.—Pacific coastal region from Requa, Del Norte County, California, north in Oregon west of the Cascades, and in Washington including the Cascades; to southwestern British Columbia.
Description.—Size large; back from near Ochraceous-Buff to near Tawny with admixture of black hair forming broad dorsal band; sides lighter than back from near Ochraceous-Buff to near Tawny; lateral line usually distinct; belly white, sometimes with faint suffusion of ochraceous on lower throat and upper chest; tail bicolored, brown above, white to yellowish-white below; ears dark, sometimes flecked with color of sides, edged with ochraceous; feet grayish-white above; palatal bridge relatively short; incisive foramina relatively long; condylobasal region long; zygomatic width great; braincase relatively broad; distance from incisors to postpalatal notch relatively great.
Comparisons.—For comparisons withZapus trinotatus montanusandZapus trinotatus eurekasee accounts of those subspecies.
Remarks.—This subspecies retains most of its diagnostic characters throughout nearly all parts of its geographic range. Intergradation occurs betweenZ. t. eurekaandZ. t. trinotatusin extreme southwestern Oregon and northwestern California (see account ofZ. t. eureka). Intergrades betweenZ. t. montanusandZ. t. trinotatushave been commented on in the account ofZ. t. montanus. Specimens from Eugene, Oregon, according to Bailey (1936:232), show affinity toZ. t. montanusbut are considered by him to beZ. t. trinotatus.
Specimens examined.—Total, 238, distributed as follows:British Columbia: Alta Lake, on Pac. Gt. Eastern Ry., 2600 ft., 5 (MVZ); Okanagan, 1 (FM);Vedder Crossing, 4 (1 MVZ, 3 PM);Chilliwack Valley, 2 (NMC); 18 mi. S Chilliwack, 1 (MVZ); Cultus Lake, 2 (NMC);Lihumption Park, 4500-4800 ft., 12 (NMC);Seymour Mtn., 4000 ft., 8 (1 MVZ, 7 PM);Cariboo, 2 (FM);Sumas, 8 (1 MVZ, 7 FM); Huntingdon, 40 (NMC);Parnassus Creek, Black Tusk Meadow, 5200 ft., 1 (PM);Howe Sound, Brackendale, 2 (NMC); Stanley Park, Vancouver, 1 (PM);Allison Pass, Manning Park, 1 (PM); Manning Park, 2 (PM).California:Del Norte Co.: Crescent City, 11 (6 FM, 5 USBS); Requa, 4 (FM).Oregon:Benton County:3 mi. N Corvallis, 2.Clatsop County: Old Fort Clatsop, 100 ft., 11 (MVZ); 71/2mi. S Cannon Beach, 50 ft., 1 (MVZ).Columbia County: 7 mi. SE Rainier, 100 ft., 11 (MVZ).Curry County: Gold Beach, 3 (FM).Douglas County: Gardiner, 7 (5 MVZ, 2 FM).Lane County: Sutton Lake, 6 mi. N Florence, 1 (MVZ).Lincoln County:Delake, 3 (2 MVZ); Newport, 2 (MVZ).Multnomah County: Portland, Council Crest, 950 ft., 1[394](MVZ).Tillamook Co.:Tillamook, 1 (MVZ);9 mi. S Tillamook, 1 (MVZ); Netarts, 3 (SDM); Blaine, 3 (MVZ).Washington County: 181/2mi. NW Portland, 1300 ft., 5 (MVZ).Washington:Clallam County: Deer Lake, 3800 ft., 3.Clarke County:31/2mi. E and 11/2N Amboy, 3500 ft., 3 (MVZ);11/2mi. ENE Amboy, 3500 ft., 13 (MVZ); 31/2mi. E and 5 mi. N Yacolt, 500 ft., 1 (MVZ);11/2mi. W Yacolt, 800 ft., 11 (MVZ).Cowlitz County:6 mi. NE Kelso, 4 (MVZ);4 mi. E mouth Kalama River, 5 (MVZ).King County: Lakeridge Tract, S end Forest Ave., Lake Washington, 2 (MVZ); Seattle 2 (MVZ); Snoqualmie Pass, 5 (MVZ).Mason County: Potlatch, 2 (MVZ).Pacific County:11/2mi. N Chinook, 10 ft., 1 (MVZ); 31/2mi. SE Chinook, 10 ft., 5 (MVZ).Pierce Co.: 5 mi. E Tacoma, 4 (MVZ); Puyallup, 3 (1 MVZ, 2 FM); Mt. Rainier, 1 (MVZ); 3 mi. E Ashford, 1 (LMH).Skamania County: Ice Caves, 2800 ft., 5 mi. WSW Guler, 1 (MVZ).Thurston County: Boston Harbor, 5 (CAS).Wahkiakum County: 4 mi. E Skamokawa, 5 (MVZ).Whatcom County: Baker Lake, 2 (MVZ).Marginal records.—British Columbia: Okanagan; Manning Park. Washington: Baker Lake; Snoqualmie Pass; Mt. Rainier; Ice Caves, 2800 ft., 5 mi. WSW Gulch. Oregon: Portland, Council Crest, 950 ft. California: Requa; Crescent City. Oregon: Gold Beach; Gardiner; Sutton Lake, 6 mi. N Florence; Newport; Netarts; Old Fort Clatsop, 100 ft. Washington: 31/2mi. SE Chinook, 10 ft.; Deer Lake, 3800 ft. British Columbia: Stanley Park, Vancouver; Alta Lake, 2600 ft.
Specimens examined.—Total, 238, distributed as follows:
British Columbia: Alta Lake, on Pac. Gt. Eastern Ry., 2600 ft., 5 (MVZ); Okanagan, 1 (FM);Vedder Crossing, 4 (1 MVZ, 3 PM);Chilliwack Valley, 2 (NMC); 18 mi. S Chilliwack, 1 (MVZ); Cultus Lake, 2 (NMC);Lihumption Park, 4500-4800 ft., 12 (NMC);Seymour Mtn., 4000 ft., 8 (1 MVZ, 7 PM);Cariboo, 2 (FM);Sumas, 8 (1 MVZ, 7 FM); Huntingdon, 40 (NMC);Parnassus Creek, Black Tusk Meadow, 5200 ft., 1 (PM);Howe Sound, Brackendale, 2 (NMC); Stanley Park, Vancouver, 1 (PM);Allison Pass, Manning Park, 1 (PM); Manning Park, 2 (PM).
California:Del Norte Co.: Crescent City, 11 (6 FM, 5 USBS); Requa, 4 (FM).
Oregon:Benton County:3 mi. N Corvallis, 2.Clatsop County: Old Fort Clatsop, 100 ft., 11 (MVZ); 71/2mi. S Cannon Beach, 50 ft., 1 (MVZ).Columbia County: 7 mi. SE Rainier, 100 ft., 11 (MVZ).Curry County: Gold Beach, 3 (FM).Douglas County: Gardiner, 7 (5 MVZ, 2 FM).Lane County: Sutton Lake, 6 mi. N Florence, 1 (MVZ).Lincoln County:Delake, 3 (2 MVZ); Newport, 2 (MVZ).Multnomah County: Portland, Council Crest, 950 ft., 1[394](MVZ).Tillamook Co.:Tillamook, 1 (MVZ);9 mi. S Tillamook, 1 (MVZ); Netarts, 3 (SDM); Blaine, 3 (MVZ).Washington County: 181/2mi. NW Portland, 1300 ft., 5 (MVZ).
Washington:Clallam County: Deer Lake, 3800 ft., 3.Clarke County:31/2mi. E and 11/2N Amboy, 3500 ft., 3 (MVZ);11/2mi. ENE Amboy, 3500 ft., 13 (MVZ); 31/2mi. E and 5 mi. N Yacolt, 500 ft., 1 (MVZ);11/2mi. W Yacolt, 800 ft., 11 (MVZ).Cowlitz County:6 mi. NE Kelso, 4 (MVZ);4 mi. E mouth Kalama River, 5 (MVZ).King County: Lakeridge Tract, S end Forest Ave., Lake Washington, 2 (MVZ); Seattle 2 (MVZ); Snoqualmie Pass, 5 (MVZ).Mason County: Potlatch, 2 (MVZ).Pacific County:11/2mi. N Chinook, 10 ft., 1 (MVZ); 31/2mi. SE Chinook, 10 ft., 5 (MVZ).Pierce Co.: 5 mi. E Tacoma, 4 (MVZ); Puyallup, 3 (1 MVZ, 2 FM); Mt. Rainier, 1 (MVZ); 3 mi. E Ashford, 1 (LMH).Skamania County: Ice Caves, 2800 ft., 5 mi. WSW Guler, 1 (MVZ).Thurston County: Boston Harbor, 5 (CAS).Wahkiakum County: 4 mi. E Skamokawa, 5 (MVZ).Whatcom County: Baker Lake, 2 (MVZ).
Marginal records.—British Columbia: Okanagan; Manning Park. Washington: Baker Lake; Snoqualmie Pass; Mt. Rainier; Ice Caves, 2800 ft., 5 mi. WSW Gulch. Oregon: Portland, Council Crest, 950 ft. California: Requa; Crescent City. Oregon: Gold Beach; Gardiner; Sutton Lake, 6 mi. N Florence; Newport; Netarts; Old Fort Clatsop, 100 ft. Washington: 31/2mi. SE Chinook, 10 ft.; Deer Lake, 3800 ft. British Columbia: Stanley Park, Vancouver; Alta Lake, 2600 ft.
Zapus princepsAllen
(Synonymy under subspecies)
Range.—The Rocky Mountains region from Yukon south into Arizona and New Mexico; westward through eastern Oregon and through the Cascades and Sierra Nevada of California; eastward in the northern Great Plains to extreme eastern parts of the Dakotas (seefig. 46).Characters of the species:External.—Size medium to large (total length 216 mm to 247 mm); tail longer than head and body (129 mm to 148 mm) and bicolored, pale brown to grayish-brown above, white to yellowish-white below; hind feet long (31 mm to 34 mm), grayish-white above; back variable from yellowish-gray to salmon-brown and ochraceous; sides paler than back; lateral line usually present but sometimes indistinct or entirely absent (when present usually clear Ochraceous-Buff); ventral coloration white, usually suffused with ochraceous; ears usually dark, sometimes flecked and usually narrowly edged with light color; guard hairs average 142 microns (130u to 168u) in diameter; underhair with medullary pigment in form of hollow squares; cuticular scales of underhair larger and fewer than in other species.Baculum.—Size medium (total length 5.6 mm to 6.6 mm); base moderately broad (0.7 mm to 0.8 mm); tip narrow (0.26 mm to 0.31 mm) rounded and dished out in dorsal aspect, blunted; shaft rounded, slightly sinusoidal, recurved at tip.Skull.—Large, not exceptionally broad and deep in relation to length; rostrum broad but tapering; pterygoid fossa moderately narrow; anterior ramus of zygomatic process usually broad; incisive foramina usually broadly rounded and elongate; auditory bullae usually moderately inflated; coronoid process of mandible relatively short. Upper premolars of medium size (averaging .55 mm in length and .50 mm in breadth), sometimes functional, with occlusal surface normally divided by single shallow re-entrant fold; m1 relatively short, narrow anteriorly.
Range.—The Rocky Mountains region from Yukon south into Arizona and New Mexico; westward through eastern Oregon and through the Cascades and Sierra Nevada of California; eastward in the northern Great Plains to extreme eastern parts of the Dakotas (seefig. 46).
Characters of the species:External.—Size medium to large (total length 216 mm to 247 mm); tail longer than head and body (129 mm to 148 mm) and bicolored, pale brown to grayish-brown above, white to yellowish-white below; hind feet long (31 mm to 34 mm), grayish-white above; back variable from yellowish-gray to salmon-brown and ochraceous; sides paler than back; lateral line usually present but sometimes indistinct or entirely absent (when present usually clear Ochraceous-Buff); ventral coloration white, usually suffused with ochraceous; ears usually dark, sometimes flecked and usually narrowly edged with light color; guard hairs average 142 microns (130u to 168u) in diameter; underhair with medullary pigment in form of hollow squares; cuticular scales of underhair larger and fewer than in other species.
Baculum.—Size medium (total length 5.6 mm to 6.6 mm); base moderately broad (0.7 mm to 0.8 mm); tip narrow (0.26 mm to 0.31 mm) rounded and dished out in dorsal aspect, blunted; shaft rounded, slightly sinusoidal, recurved at tip.
Skull.—Large, not exceptionally broad and deep in relation to length; rostrum broad but tapering; pterygoid fossa moderately narrow; anterior ramus of zygomatic process usually broad; incisive foramina usually broadly rounded and elongate; auditory bullae usually moderately inflated; coronoid process of mandible relatively short. Upper premolars of medium size (averaging .55 mm in length and .50 mm in breadth), sometimes functional, with occlusal surface normally divided by single shallow re-entrant fold; m1 relatively short, narrow anteriorly.
Fig. 46.Distribution ofZapus princeps.Guide to subspecies1.Z. p. cinereus7.Z. p. oregonus2.Z. p. curtatus8.Z. p. pacificus3.Z. p. idahoensis9.Z. p. princeps4.Z. p. kootenayensis10.Z. p. saltator5.Z. p. luteus11.Z. p. utahensis6.Z. p. minor
Fig. 46.Distribution ofZapus princeps.
Guide to subspecies
Geographic Variation
There are 11 subspecies recognized, most of which are in the mountains of the western United States and southwestern Canada. There is geographic variation in color, relative proportions of external parts (tail, hind feet, head, and body), and shape and size of the skull.
Three basic types of coloration occur inZ. princeps, as pointed out by Hall (1931:9). Yellow-sided dark-backed jumping mice exemplified bykootenayensis,idahoensis, andutahensisare found to the eastward in the Rocky Mountains. Reddishbrown-sided, brown-backed jumping mice typified byluteusandpacificusare found to the westward in the Sierra Nevada and in New Mexico and Arizona; mice with yellowish-buff or pinkish-buff-sides and light backs are the subspecies,cinereus,curtatus, andoregonus, that occur in the intervening Great Basin.
External dimension as a whole decreases from north to south, although not uniformly. For example, the smallest individuals are of the southernmost geographic subspecies (Z. p. luteus), but the largest are of the subspecies (Z. p. utahensis) that is near the geographic center of the range for the species. In the skull there is geographic variation in the length and shape of the zygomata, size and shape of the incisive foramina, alignment of maxillary tooth-rows, size and shape of auditory bullae, position of the postpalatal notch in relation to M3, and the presence or absence and size of the medial projection on the inferior ramus of the zygomatic process of the maxillary.
NATURAL HISTORY
Habitat.—Zapus princepsoccurs most commonly adjacent to streams where grasses and herbs are in lush growth. It frequents mountain meadows neighboring small streams and is often taken from alder, aspen, or stands of willow, where the moist ground supports a heavy undergrowth of herbs. Davis (1939:330) found these mice in heavy herbage along a small stream bordered by quaking aspen near Victor, Teton County, Idaho. They were found along streams bordered by willow, rose, alder, huckleberry, sedges, and herbs of various kinds at Alturas Lake, Mill Creek, and at the head of the Pahsimeroi River. Linsdale (1938:195) found jumping mice in the Toyabe Mountains, Nevada, near the streamsides or in seepy areas close to the streams where associated vegetation included rose, willow, wild peach, sage, grasses, and herbs. In the Uinta Mountains,Utah, R. D. Svihla (1931:264) obtained them from willows along streams in mountain parks. Borell and Ellis (1934:37) in the Ruby Mountains, Nevada, found jumping mice to be common in heavy vegetation along streams. Louise Kellogg (1916:369) obtained jumping mice in northern California; all were near water, in grassy meadows, or under alders where vegetation was dense.
Zapus princepsis locally abundant, but its numbers seem to vary considerably from year to year as well as seasonally. Early autumn, when young of the year are abroad, seems to be the period of greatest abundance. Moore (1928:154) remarks that runways were plainly marked and well strewn with four-inch pieces of brome-grass. Davis (1939:334) notes thatZ. princepshas runways, and found that sections, four inches long, of cut grass piled in runways was good evidence of the presence of the mouse.
Behavior.—In reference to locomotion ofZ. princeps, Davis (loc. cit.) writes, “In rapid progression jumping mice move by a series of zigzag hops. One young of the year found in tall grass near Victor made horizontal leaps of approximately three feet. The zigzag course was difficult for me to follow, and I was led to wonder if this mode of locomotion were not advantageous to the mice in eluding animals that would do them harm.” Hollister (1912:26) remarked thatprinceps, when startled, sometimes jumps five to six feet at a bound. Concerning the swimming ability ofZ. princeps, Bailey (1936:233) quotes from Hollister’s notes, “While I was walking around the grassy border of a small pond one jumped out at my feet and struck in the water like a frog, which at first it was thought to be, until it was seen swimming across the pond on the surface of the water … he certainly handled himself as if perfectly at home and swam with little effort and great speed over the still surface of the pond.” Davis (1939:334) obtained two individuals at Mill Creek, Idaho, in traps placed on artificial islands of stones in the middle of the creek where the water was about six inches deep. He speculated that the only way the mice could have reached the traps was by swimming. Grinnell, Dixon, and Linsdale (1930:531) record an individual which was seen hopping in the inch-deep water of a small stream at Lake Helen, California.
According to Hollister (1912:26) and Davis (1939:335), jumping mice are for the most part nocturnal, but occasionally they are seen by day in tall grass.
Little is recorded concerning the hibernation ofZ. princeps. What data are available suggest that, starting in July, these animalsaccumulate a heavy layer of fat on the inside of the skin with especially large amounts in the inguinal region. By August or early September, animals are excessively fat, and the start of hibernation is dependent then upon the arrival of a heavy cold snap. Grinnell, Dixon, and Linsdale (1930:531), in their study of the vertebrates of the Lassen Peak region of California noted that the latest activity by these mice was September 13. As regards the time of onset of hibernation in Idaho, Davis (1939:336) states that, “I know of no records of capture later than September and infer that hibernation begins in that month or the next.” Bailey (1932:227) writes that in New Mexico, animals obtained on September 20 were very fat, probably were ready to hibernate at the first cold wave, and had winter nests in burrows well underground.
Enemies.—Bailey (loc. cit.) lists hawks, owls, and weasels as natural predators onZ. princeps. Stanford (1931:362) records the garter snake (Thamnophis) as a predator of jumping mice. A large snake of this genus obtained by him regurgitated two jumping mice a few hours after its capture. Grinnell, Dixon, and Linsdale (1937:232) report that on Parker Creek, in California, H. C. Bryant frightened a weasel that dropped a freshly killed jumping mouse. Crowe (1943:407) reportedCuterebrafly larvae in the inguinal region of aZ. princepsobtained at Invermere, British Columbia. Several mice of this species taken at Moccasin Lake, 19 mi. W and 4 mi. N of Lander, 10,000 ft., Fremont County, Wyoming, were heavily infested with mites of the family Laelaptidae.
Food.—In early September in central Utah, Moore (1928:154) found only a white, starchy, glutinous paste in stomachs of sixZ. princepsand only traces of a brown seed coat in a seventh. The main seeds eaten seemed to be from an introduced brome-grass which was abundant in the vicinity of capture. Bailey (1932:226) wrote ofZ. princepsin New Mexico, that “In feeding they cut down the tall grass, beginning at the bottom and cutting the stem at intervals as high as they can reach until the seed part of the grass is brought down.” He (op. cit.:227) remarked that the food was almost entirely seeds of grass and grasslike plants and that the stomach contents almost always were perfectly clean white dough from the shelled kernels of small seeds.
Reproduction.—Females with embryos have been collected from late May to mid-July and lactating individuals until late August. Possibly there is only one litter per season as Davis (1939:336) suggests is the case in Idaho.
Embryos in 25 pregnant females averaged 5 (2-7). The mammae of the female are arranged in four pairs (two abdominal, one pectoral, and one inguinal).
Z. princepsbuilds a grass nest on the ground which is placed under cover of vegetation or surface litter. Bailey (1932:227) writes that in New Mexico jumping mice of this species use fibers of grass to construct a ball-shaped nest. The nest usually has one opening but sometimes there are two. In the Ruby Mountains, of Nevada, Borell and Ellis (1934:37) found the globular nests of this mouse on the ground in tall grass.